Participants will be randomized in a double blind fashion to receive either abciximab (ReoPro) or placebo intravenously over 12 hours. Randomization will be stratified by sickle cell genotype: Sickle Cell Anemia (SS) vs. Sickle-Hemoglobin C Disease (SC). All patients will receive standard supportive care, including hydration, supplemental oxygen as needed to maintain oxygen saturation >92%, scheduled use of NSAIDS, and narcotics titrated to effect.